Technical Abstract:
Tolerance refers to the ability of certain susceptible plant lines to tolerate a disease, as measured by a less adverse effect on yield than observed in most other susceptible lines with the same level of disease. Experiments were conducted in Quincy, FL, between 2006 and 2008 to test for tolerance to soybean rust (caused by Phakopsora pachyrhizi) among 10 to 12 soybean cultivars developed by public sector breeding programs in the southeastern U.S. In comparisons of fungicide-protected plots versus unprotected plots, significant differences in percent yield loss were observed among the cultivars, which were from maturity groups VI to VIII. In 2008, when the local soybean rust epidemic in Quincy was both early and severe, yield losses ranged from 50.4% in the University of Georgia line G00-3309 to 82.5% in the cultivar Kuell. Percent yield loss was not correlated with maturity in 2008. Further investigations are being conducted to determine whether the cultivars with the lowest yield losses are truly tolerant rather than partially resistant to soybean rust.